The present invention relates to a method of producing a laminated film for forming a titanium oxide film etc. on a polymeric film by plasma CVD method as well as an anti-reflective film obtained by the method.
Transparent substrates such as glass and plastics are used in various displays such as liquid crystal displays, plasma displays and CRT used in computers, word processors, television sets and display plates, displays for instruments etc., rearview mirrors, goggles and window glasses. Letters, figures and other information are read through such transparent substrate, but if light is reflected by the surface of the transparent substrate, there arises the problem that the information is hardly read.
Accordingly, the substrate is endowed with anti-reflective functions. As the method of endowing it with anti-reflective functions, there is a method wherein an anti-reflective film consisting of inorganic compounds such as silicon oxide (also referred to hereinafter as xe2x80x9csilicaxe2x80x9d), zirconium oxide, titanium oxide and magnesium fluoride is formed directly on a transparent substrate by various methods. In particular, titanium oxide has high refractive index and is thus preferably used in a highly refractive layer in an anti-reflective film. However, if an anti-reflective film containing titanium oxide etc. is to be formed directly on a transparent substrate, there are many limitations on the size, thickness and shape (curved surface etc.) of the formable transparent substrate.
Accordingly, a method has been proposed in which an anti-reflective film consisting of a titanium oxide film etc. is formed on a transparent polymeric film and the resulting polymeric film having the anti-reflective film formed thereon is attached to a substrate requiring anti-reflective functions. According to this system, the limitation on the shape of the transparent substrate can be significantly reduced, while the cost for conferring anti-reflective functions on the surface of the transparent substrate can also be reduced.
As the means of forming an anti-reflective film such as titanium oxide film etc., there are methods such as vacuum deposition, sputtering, thermal CVD method, and wet coating in a sol-gel method. However, when a titanium oxide film is to be formed on a polymeric film by these methods, there occur the following problems.
In vacuum deposition with titanium or titanium oxide as the raw material, the adhesion thereof to the substrate is poor. In sputtering using titanium and titanium oxide as the target, there arises the problem of e.g. a very low rate of formation of a titanium oxide film.
Because thermal CVD method is a method in which a thin film is formed by oxidization and decomposition of starting gas by heat energy of a substrate, the substrate should be heated at high temperature. For example, the temperature of the substrate for forming a titanium oxide film by thermal CVD method should be about 300 to 500xc2x0 C. Since application of such high temperature to the polymeric film substrate causes decomposition and oxidization of the polymer compound therein, thermal CVD method cannot be used for forming a titanium oxide film on the polymeric film.
In the case where a titanium oxide film is formed by wet coating in a sol-gel method etc., it is difficult to provide the titanium oxide film as a thin film with constant qualities and regulated thickness. To use the titanium oxide film as an anti-reflective layer, a uniform thin film with a thickness of several tens nm to several hundred nm should be formed on a substrate with prescribed thickness without dispersion of the thickness; otherwise, the intended optical functions in design could not be demonstrated. However, if a titanium oxide film is formed as an anti-reflective layer by the means of wet coating in the sol-gel method etc., it is difficult to satisfy such strict conditions.
The present invention was made under these circumstances. In the case where an anti-reflective titanium oxide film etc. are to be formed on a polymeric film substrate, the object of the present invention is to provide a method of producing a laminated film, wherein the laminated film having optical performance usable as an anti-reflective film can be formed at a high rate and at a temperature at which the polymeric film is not decomposed, elongated or deformed, as well as an anti-reflective film obtained by the method.
To achieve this object, the present invention provides a method of producing a laminated film, wherein at least one layer of titanium oxide film is formed on a polymeric film having a temperature regulated in the range of xe2x88x9210 to 150xc2x0 C. by means of a plasma CVD device capable of controlling the temperature of the polymeric film.
By using plasma CVD method in forming a titanium oxide film on a polymeric film, the surface temperature of the film can be maintained in the range of xe2x88x9210 to 150xc2x0 C. whereby the titanium oxide film can be formed without causing decomposition, elongation and deformation of the film. Plasma CVD method is a method of forming a film by utilizing the phenomenon where plasma is generated in a reaction chamber in which a prescribed gas is introduced, whereby atomic or molecular radical species are generated to adhere to a solid surface, and in the surface reaction, further volatile molecules are often released and incorporated into the solid surface.
Further, in the present invention, at least one layer of silica film may be formed on the polymeric film having a temperature regulated in the range of xe2x88x9210 to 150xc2x0 C. by means of the plasma CVD device.
In the present invention, this plasma CVD device is preferably a device including at least a reaction chamber to be introduced starting gas, a film forming drum capable of temperature control, and plasma generating means for generating plasma between the plasma generating means and the film forming drum, and in this plasma CVD device, a webbed polymeric film is continuously conveyed by the film forming drum to the reaction chamber having starting gas introduced into it thereby controlling the temperature of the polymeric film and simultaneously forming a film on the polymeric film.
By use of such a device, a titanium oxide film or a composite film consisting of a titanium oxide film and a silica film can be formed successively on the webbed polymeric film, particularly on the continuous length film. Further, the film is conveyed by the film forming drum and simultaneously the titanium oxide film etc. are formed on the film forming drum. Accordingly, the temperature of the polymeric film can be regulated by controlling the temperature of the film forming drum, thus permitting a film to be formed thereon under low-temperature conditions not causing deformation etc. of the film. The plasma generating means includes a coil, an antenna, and an electrode connected to a power source, or a window for introduction of electromagnetic wave.
In the plasma CVD device, a plurality of reaction chambers may be arranged along the outer periphery of the film forming drum. Arrangement of a plurality of reaction chambers is advantageous because if e.g. starting gas as the starting material of a titanium oxide film and starting gas as the starting material of a silica film are introduced respectively into the separate reaction chambers, a titanium oxide film and a silica film can be produced in one operation. Further, a plurality of film forming drums may also be arranged.
Further, the present invention provides an anti-reflective film wherein at least one layer of titanium oxide film having a refractive index of 2.0 or more to 2.9 or less (wavelength xcex=550 nm) is laminated by plasma CVD method on a polymeric film.
Since the titanium oxide film laminated on the polymeric film has been formed by plasma CVD method, the resulting product is a high-quality anti-reflective film in which the titanium oxide film has necessary refractive index and the polymeric film is not deteriorated. In addition, the required optical characteristics of the titanium oxide film are that its refractive index is 2.0 or more (wavelength xcex=550 nm). This is because if the refractive index is less than 2.0, the titanium oxide film cannot be perfectly formed, thus failing to satisfy the required criteria of a product as an anti-reflective film. On the other hand, the upper limit of the refractive index of the titanium oxide film in the present invention is defined to be 2.9 because usually the refractive index of the titanium oxide film cannot be 2.9 or more (wavelength xcex=550 nm),
In the anti-reflective film of the present invention, a silica film may be laminated by plasma CVD method on the face of the titanium oxide film formed on the polymeric film.
In the present invention, the outermost layer is preferably the silica film described above. This is because the silica film has lower refractive index than that of the titanium oxide film and low reflectance, and thus its use as the outermost layer of the anti-reflective film brings about a high anti-reflective effect. Further, because the surface energy of the silica film is relatively low, it has stain resistance and water repellency. Accordingly, it can also confer stain resistance and water repellency on the anti-reflective film.
In the anti-reflective film of the present invention described above, it is preferable that a hard coat layer is formed on the polymeric film, and a layer formed by plasma CVD method is laminated on the hard coat layer. By providing the hard coat layer in this manner, the anti-reflective film can be endowed with scratch resistance.
Further, an intermediate-refractive layer is preferably formed on the hard coat layer. By forming the intermediate-refractive layer in this manner, the anti-reflective effect can be improved.
In the anti-reflective film of the present invention, the polymeric film is preferably a monoaxially or biaxially oriented polyester film or a triacetyl cellulose film. The polyester film is excellent in transparency and thermostability and can thus be used as an anti-reflective film in various utilities, and the triacetyl cellulose film does not have optical anisotropy and is thus suitable as an anti-reflective film like the polyester film.
By using plasma CVD method in forming a titanium oxide film, a silica film etc. on a polymeric film as described above in the present invention, the surface temperature of the film can be maintained in the range of xe2x88x9210 to 150xc2x0 C. whereby the titanium oxide film can be formed without causing decomposition, elongation and deformation of the film. Further, the silica film has lower refractive index and reflectance than those of the titanium oxide film, and thus its use as the outermost layer of the anti-reflective film brings about a high anti-reflective effect. In addition, because the surface energy of the silica film is relatively low, it has stain resistance and water repellency. Accordingly, it can also confer stain resistance and water repellency on the anti-reflective film. As described above, the film formed according to the present invention is suitable for use as an anti-reflective film.